Abundant Evolution Processes of Polaron-Pairs and Exciplex States with Various Electron–Hole Coupling Distances in Exciplex-Based OLEDs by Modifying Device Hole-Injection Abilities

作者：Xi Zhao, Jing Chen, Li-Hong Cheng, Yang Song, Bo Wang, Teng Peng, Junhong Liu, Hong Lü, Sijie Zhang, Zuhong Xiong · 发表于：ACS Photonics · 年份：2023 · DOI：10.1021/acsphotonics.3c01315 · 被引用次数：18 · 研究领域：Organic Light-Emitting Diodes Research、Organic Electronics and Photovoltaics、Thin-Film Transistor Technologies

Intersystem crossing (ISC) and reverse ISC (RISC) between singlet and triplet polaron-pairs (PP) and exciplex (EX) states, triplet-charge annihilation (TCA), and triplet–triplet annihilation (TTA) are well-known key spin-mixing processes in EX-based organic light-emitting diodes (EX-OLEDs) for improving the device optoelectronic performances. These microscopic processes usually show normal current dependencies; i.e., ISC and RISC weaken while TCA and TTA enhance with increasing bias current, respectively. Here, planar- and bulk-heterojunction EX-OLEDs (PHJ- and BHJ-EX-OLEDs) with good and poor hole-injection abilities were fabricated by modifying the device hole-injection layer. Amazingly, electroluminescence (EL) spectra are used to find that electron–hole coupling distances ( r ) of PP and EX states in PHJ-EX-OLEDs with good and poor hole-injection abilities are short and long, respectively. This unreported phenomenon only exists in PHJ-EX-OLEDs because holes and electrons separately accumulate on different sides of the donor/acceptor interface, and the distance from holes to the interface increases with decreasing hole-injection ability. However, r of PP and EX states in BHJ-EX-OLEDs are always short whether the devices have good or poor hole-injection abilities since holes and electrons are mixed together within the donor:acceptor blend layer. Furthermore, magneto-EL (MEL) traces of these devices are used as fingerprint detection techniques to distinguish various current-...